As a pressure foot of a printed circuit board drilling apparatus for drilling printed circuit boards, for instance, pressure feet disclosed in Japanese Patent Unexamined Publication No. 63-300807, Japanese Patent Unexamined Publication No 3-3713 (corresponding to U.S. Pat. No. 5024562), and so forth have been proposed.
These pressure feet are designed such that compressed gas is ejected toward a drill bit from a groove formed in a lower end portion of the pressure foot, and that the drill bit is cooled by the compressed gas.
Increasing the machining speed and decreasing the frequency of replacement of the drill bit are expected for enhancing the productivity. Improving the quality of drilled holes is expected for responding to an increase in accuracy of equipments in which printed circuit boards are used, and suppressing generation of offensive odor caused by burning of printed circuit boards is expected for improving the operation environment.
They are subject matters which can be solved by increasing the cooling efficiency of the drill bit. In the prior art, however, cooling of the drill bit is effected by heat conduction through the compressed gas injected into the pressure foot, and consequently, it is impossible to expect the cooling efficiency of the drill bit to be largely enhanced.